Photocatalytic degradation of salicylic acid and caffeine emerging contaminants using titania nanotubes

- Titania nanotubes with 5-20 μm length synthesized under galvanostatic anodization.
- Close to 50% photocatalytic degradation of caffeine and salicylic acid was attained.
- 10 μm nanotubes length was optimum for photocatalysis.
- Small dependence of photocatalytic efficiency on solutions pH attained.
- TNT films give reproducible activity after 10 photocatalytic cycles.

Heterogeneous photocatalysis can be a suitable add-on process to conventional wastewater treatment methods aiming to the full degradation of emerging contaminants contributing to water pollution. This work examines the photo-degradation of two frequently detected emerging contaminants (caffeine and salicylic acid) using titanium dioxide nanotubular films (TNTs) so as commercial TiO2 nanoparticulate films (Evonik P25) for comparison. The TNT films were prepared by electrochemical anodization of titanium metal and reached lengths of 20 μm, with a high growth rate (10 μm/h). They present an open porous structure with large specific surface area suitable for efficient adsorption of the contaminants and formation of a large number of photocatalytic active sites. After calcination at 450 °C, TNT films obtain the anatase crystal structure, absorb well in the UV range and present significant photocatalytic activity with high degradation rates for both examined emerging pollutants. Furthermore, they present small variability of their photocatalytic efficiency in a big range of the solutions pH values and under consecutive photocatalytic cycles, rendering them suitable at various wastewater treatment conditions.